after I added to my system (AC500 + 4x B300S) two more B300S batteries,
the batteries are extremely unbalanced.
…
Please see the photo and the figure: I started with 100% for all batteries.
After a few days with overall SOC between 55 - 85 % there are now (SOC is 58%)
two nearly full batteries (94%), one completely (0%, for the second day) and one nearly empty (8%).
Obviously there is no significant current between the batteries or precisely, towards the empty batteries.
…
All batteries have the same BMS 1022,09.
Checking for updates I’m told that there is none - but I read in the forum that there is the version 1022,14. Software Update Notification for B300 and B300S
They say only for SN AC5002247, AC5002248.
My SN is AC5002308.
…
How can I get the new software for the batteries?
Will it help?
…
Otherwise, I must buy a T500 adapter to recalibrate each single battery.
Though I’m not convinced that it will help because, as I said at the beginning,
the problem got worse with 6 batteries. (Even with 4 batteries, it was not
well balanced.)
…
Now with one or nearly two batteries empty I’m anxious that it can reduce
their life time.
Try to charge all of them to 100%. If one of the batteries fails to accept a charge, try connecting it to your AC500 alone. You can use the Bluetti App to check if your power station or batteries have a firmware update available. Connect via bluetooth.
You can mention here all the serial numbers of your AC500 device and all batteries and then @mention Bluetti support employee to have them verify if you have the latest firmwares for your hardware revisions.
Please read this thread for tips on getting this issue resolved. It’s with an AC300 but those devices are very much similar.
This includes a realibration of every battery, where it is important that every battery reaches full state, 100% with no more charging and 0%, until the AC500 shuts down. Don’t leave the batteries empty after a full discharge. Recharge them again.
If that does not help, ask support for more options.
It is normal that there are some differences between battery SoC levels, roughly 10% to 20%, but having one at 0% and others ate 94% is bad…
Hi @digait, We have arranged a firmware upgrade for you, and the latest BMS updates will be pushed to your device within 24 hours. Please upgrade the firmware tomorrow.
When updating, ensure only one battery is connected at a time, as each B300S battery needs to be updated individually. After all of them are updated, calibrate the battery. This should help resolve the issue.
Please follow the steps below to recalibrate it:
Please discharge all the power (charge AC & DC appliances with the power station) until the SOC is 0%, turn off the machine, and leave it for 3 hours till it cools down.
Please charge it again, please do not load any device when charging it, and do not interrupt it while in charge.
This is the first I heard about waiting 3 hours for cooldown. I thought it was bad to leave them discharged for too long.
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Since it’s winter electric heaters are HUGE power drains and good for discharging batteries. In fact, I should recalibrate mine as I have 3 heaters.
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You might want to point out to them that don’t just go by the SOC reading 0%; discharge it until the AC500 shuts down on it’s own.
Hi @St8kout, Yes, after a complete discharge, enough cooling time is needed.
Even in cold winter, the internal temperature of the battery can still rise significantly due to its operation, and the heat dissipation is slower because of the casing.
Thank you for your addition, it is very helpful and provides valuable insights.
Burn them all down to zero and the ac500 actually shut off. Then charge back up. Supposedly, every time you add a new battery, to calibrate them all together, you need to drain them all , shut-off, and then recharge back up to 100.
Works for me, just sayin.
See figure for position of the batteries.
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It seems that again the same two batteries (#2 and #6) are those which
are not charged resp. will be charged at last.
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I noted (yesterday and this morning, when PV charging started, 150 W input),
that the batteries most full (#4 and #5) were charged, all others remained in
standby.
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I hope this information can help in any way to find a solution (-> BMS update
or also an update for the AC500?).
.
Hi @digait, We really want to help you, but your firmware is already up to date.
We have made efforts to minimize the gap using new firmware; however, the SOC differences still objectively exist. Due to slight variations in battery version batches, voltage differences are also inevitable, which results in inconsistent charging and discharging speeds.
In our view, this difference is within an acceptable range and will not significantly impact actual usage.
If the entire system can charge to 100% and discharge to 0%, we consider it to be functioning normally.
The SOC difference arises due to the inherent characteristics of the product. Our batteries use premium lithium iron phosphate (LiFePO4), which is exist the inconsistency among cells. This inconsistency stems from the high internal resistance of LiFePO4 batteries. Each cell’s internal resistance varies slightly, causing some energy to be consumed by internal resistance during charging and discharging. Over time, this leads to increasing discrepancies in the charge levels of individual cells.
Additionally, during the redox reactions, ferrous iron (Fe²⁺) may oxidize to ferric iron (Fe³⁺) or reduce to metallic iron, potentially altering the internal resistance of the battery.
Coupled with SOC measurement error, overcharging or over-discharging individual cells can further affect internal resistance. This may eventually result in varying SOC levels among the four cells in a battery, which is a common manifestation of LiFePO4 cell inconsistency.
I would also like to comment on the problem.
I am currently running an AC500 with 3xB300 and 1xB300S.
In my experience, the deviation depends on the power of the charge or discharge.
If this is relatively low, for example under 300W, not all batteries are charged or discharged evenly at the same time. The more often and longer this happens, the greater the deviation.
I suspect that the SOC of the batteries is not measured but is calculated from the sequence of charging and discharging power.
I also noticed that the charging process to 100% occurs in jumps. By this I mean that the batteries do not always charge evenly to 100% SOC.
I observed that one battery had reached 100% SOC, all the others suddenly jumped to 100%, even though they had only reached 75%, 85% or 95%, for example.
The conclusion for me is that the SOC displayed on the batteries does not match their actual charge level. Since the 4 batteries are all electrically connected in parallel, their charge level should not differ significantly from one another, since they should all be charged or discharged at the same time and evenly. Perhaps the Bluetti technicians could comment on this.
That’s why I no longer worry about the SOC values displayed, but only use them as an approximate guideline. I simply let the system run and charge it up to 100% every now and then.
Then the SOC is correct again for a while.
The calibration [0%-100%] is very time-consuming and only provides a short-term solution to the problem.
Right now, the SOC of the batteries is 80%-47%-10%-53%.
The total SOC displayed is 47%. There is no feed-in and consumption is currently 170W.
All batteries are currently showing standby, even though they are discharging.
Perhaps you can share your experiences.
Three batteries are currently charging but the one with the lowest SOC (Nr.4) remains in standby. I wonder why such a different SOC occurs even though all batteries are connected in parallel.
Maybe BLUETTI_CARE could say something about this.
Sorry, but I cannot share your opinion.
If, over some days, input power equals output power the two batteries with the lowest SOC will inevitably run into a 0% state. It seems that they are charged last and discharged first.
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Today, a very sunny day, I reached 88% overall SOC - with 99% max. and 72% min.
This evening, consuming a lot, at the moment the overall SOC is 57% with SOC max. 81% and SOC min. already at 26% (27% the second low battery).
To prevent that the most empty batteries will be drained completely, I switch them off over night.
But this can’t be the solution!
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You tell something about inconsistency and internal resistance of cells:
As this problem is known to you why isn’t there a comunication between power station and batteries
in order that the power station compares the SOC of the batteries and controls their BMS?
I will add some further screenshots showing the status of the batteries.
I can’t help, I don’t understand what is going on.
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Figure 1
Very early in the morning, PV input only about 200 W, no AC output.
Battery 2, 4 and 6 are charging, but (the problematic) batteries 3 and 5 are discharging.
(Sorry, the screenshot did not capture battery 1.)
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Why is there a current FROM the batteries 3 and 5 with the lowest SOC (41%, 45%)
to batteries with a higher SOC (70%, 78%, 86%)?
.
.
Figure 2 (time 19:39) and 3 (time 21:56)
In the evening, AC output between 250 and 500 W
.
The batteries 2 to 6 are discharging, but battery 1 charges! From 72% to 76% after ca. 2,5 h
whereas the batteries 3 and 5 with the lowest SOC are discharging (from 49% to 40% and
from 57% ot 48%).
Again, there is no current towards the batteries with the lowest SOC.
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Just speculating: Could it be that the PV input wattage is not high enough to overcome the internal power use of your AC500 and your 6 batteries? This equipment has quite a substantial internal energy consumption. Especially when the inverter is turned on.
